The invention relates to a roller head for a resistance seam-welding machine, having a stator, an electrode roller which is rotatably mounted as a rotor on the stator, a sliding contact current transmission device arranged between stator and rotor and is urged against at least one of them by spring force, and ducts for passage of a coolant in the stator, the rotor and the sliding contact current transmission device, the sliding contact current transmission device comprising at least one annular disc which extends radially between rotor and stator and is flexibly designed in its intermediate bridging part between the inner and outer circumferences, in accordance with U.S. Pat. application No. 667,021, filed Mar. 7, 1991.
Such a roller head, which forms the subject matter of the aforementioned patent application, represents a modification in comparison with roller heads of the type known from U.S. Pat. No. 3,546,655 and U.S. Pat. No. 3,596,225, which are not suitable as a substitute for fluid roller heads which are known, for example, from CH-A No. 639 548 and U.S. Pat. No. 4,181,523. Such fluid roller heads are used for welding inside narrow can bodies. Between the stator and the rotor is provided an annular gap, in which there is a fluid metal, for example, quicksilver or a gallium alloy, which serves for current transmission from the stator to the rotor. As such roller heads require careful sealing and constant checking of this sealing, and as the fluid metals used are not particularly good heat conductors, and by comparison with copper, are not good electrical current conductors, and moreover, with the use of a gallium alloy, problems may arise because this metal alloy solidifies at temperatures not very far below room temperature, an attempt is made to avoid fluid as a sliding contact current transmission device and replace it by non-fluid metallic sliding contacts. As the abovementioned known roller heads with an internally situated sliding contact current transmission device are inferior to fluid roller heads in regard to current transmission capacity and length of life, because they have costly brush constructions as a sliding contact current transmission device or as a component thereof, the roller head according to U.S. Patent application Ser. No. 667,021 has been provided, which in regard to assembly dimensions, current transmission capacity and length of life, is comparable with the fluid roller heads which have been used up to now and which it is intended to replace, and the sliding contact current transmission device between stator and rotor also has a contact pressure which remains practically uninfluenced by vibrations, eccentricity etc. This is achieved because the sliding contact current transmission device is composed of at least one annular disc, which extends radially between rotor and stator and is flexibly designed in its intermediate part between rotor and stator. Moreover, the roller head according to the U.S. Patent application Ser. No. 667,021 manages with a minimum number of comp which considerably reduces manufacturing costs, maintenance expenditure and wear.
Practical use of the roller head according to U.S. Patent application No. 667,021 has shown that there is a great demand for the current transmission principle of this roller head to be made usable in other spheres.
The problem of the invention is therefore to broaden the area of application of the roller head.